Flippost

Closes #206 and #191

See merge request STJr/SRB2Internal!320

Change flipped starpostz to define the top of the player object, for cases where scale on contact with starpost is different to spawn scale.

Newegg dot blag

See merge request STJr/SRB2Internal!305

* Store gravflip (resolves #206) and destscale in starposts. (Using the same field, taking advantage of the fact that object scale will always be positive!)
* Update the function signature of P_MixUp to accomodate both it and drawangle instead of doing it outside of the function.
* If the player is spawning from the start of the stage and it's from the ceiling, be in fall frames as requested (resolves #191).

Minor musicplus-related fixes

See merge request STJr/SRB2Internal!310

Ignore bots when looking for a player

Closes #190

See merge request STJr/SRB2Internal!301

Fix -skipintro in OpenGL

See merge request STJr/SRB2Internal!308

DEVMODE: 2D toggle command

See merge request STJr/SRB2Internal!309

* Comment out the notices that the two types of music are disabled (see issue #179; not a perfect fix, but good enough for now).

* Fix jingle captions dying immediately (caused by an S_StopMusic call in P_PlayJingle; resolved by modifying order of operations).

Give the Spectator Eggrobos the ability to move left and right relative to their angle, with initial direction depending on MTF_OBJECTSPECIAL/MTF_AMBUSH flag presence. (May need more tweaking before putting in CEZ3)

Motor's new Eggman sprites, along with some other sweet bits of boss polish. What else can I say? Just play it.

Weapon ammo penalty indicator

See merge request STJr/SRB2Internal!297

Autobrake polish

Closes #176

See merge request STJr/SRB2Internal!293

P_PlayerCanDamage fix

See merge request STJr/SRB2Internal!291

# Conflicts:
#	src/d_netfil.c

Compare the file name only for real

See merge request STJr/SRB2!511

Calling all Lua consvars

See merge request STJr/SRB2!509

CL_SendRequestFile prepends the path for each file.

GFZ boss rework + boss explosion fun

See merge request STJr/SRB2Internal!290

* Make it actually look like a brake, so people can tell it's on instead of just having high friction.
* Fix it fucking with spring chains (caused by being unwittingly active for the first tic of spring collision).

Added quick validity checks for three linedef executor specials that require a player mobj to be the triggerer (432, 434 and 437)

* Make sure the consvar's properties are all initialised to zeros as defaults
* Error if the consvar is not given a name
* Error if the consvar has CV_CALL but no call function
* Error if the consvar has CV_NOINIT but not CV_CALL

MI cleanup returns

See merge request STJr/SRB2Internal!292

Fix all our landing woes. (For now.)

See merge request STJr/SRB2Internal!289

# Conflicts:
#	src/config.h.in
#	src/d_clisrv.c
#	src/d_netcmd.c
#	src/doomdef.h
#	src/p_map.c
#	src/p_maputl.c
#	src/sdl12/macosx/Srb2mac.xcodeproj/project.pbxproj